The invention relates to purification and fractionation of pectin-containing vegetable material, especially sugar beet pulp. The invention relates particularly to separating pectin and pectic sugars/oligomers and simultaneously salts from pectin-containing sugar beet pulp by using separation methods based on the molecular weight, such as ultrafiltration and chromatographic fractionation.
Pectin is a commonly used additive in food industry. It is useful, for example, as a stabilizing agent, thickener and gelling agent in, for example, jams and other fruit-based products as well as in sour milk-based products, such as yoghurts.
For the separation of pectin, the vegetable material used as a starting material, such as sugar beet pulp, is first brought into a soluble form by using, for example, acidic or basic hydrolysis. During the hydrolysis, salts are introduced into the solution which are usually undesired in the final pectin product and which should thus be removed.
Pectins have conventionally been produced from apples, sugar beet pulp or the citrus peel by first extracting soluble polymers with acid, whereafter the obtained solution is filtered and concentrated and the pectins are precipitated with alcohol or metal salts at a suitable pH. Free sugars remain in the alcohol-water solution. Since the amounts of solvent utilized in the method are large, the sugar content in the alcohol-water solution is extremely low.
In addition to pectins, the sugar beet pulp includes valuable sugar components, such as L-arabinose. In accordance with the methods known hitherto, the simultaneous separation of pectin and sugar components has been difficult, e.g. for the reason that when separating sugars, pectin has a tendency to be destroyed. On the other hand, in the earlier methods for separating pectin, the sugar/oligomer components are not normally recovered.
A previous method to produce pectin from a sugar beet pulp hydrolysate is disclosed in SE-B 453511 (Nils Monten). This method uses anion exchange to purify the sugar beet hydrolysate. The method results in an impure pectin solution, not purified pectin.
JP Patent 56 011 903 (Chisso Corporation) describes the use of ultrafiltration for separating xe2x80x9ccrudexe2x80x9d pectin from vegetable material. The starting material is first treated with hydrochloric acid at a pH 2.5 to 3.0, and pectin is extracted at a temperature of 85xc2x0 C. The obtained product is purified by filtration, and the filtrate is ultrafiltered by using a membrane having a cut-off size of 6000 to 20000 Da.
U.S. Pat. No. 5,008,254 (Weibel, M. K.) discloses a method wherein fast acidic hydrolysis is conducted at a high temperature (120xc2x0 C.) for a short period of time (six seconds) in order to recover a pectin-sugar mixture from sugar beet pulp. The hydrolyzed mixture containing sugars and some pectin compounds is concentrated by ultrafiltration (cut-off size 30000 Da). Said fast acidic hydrolysis is extremely complex technically, and the insoluble fibres which remain when the acidic hydrolysis is used tend to disintegrate into colloidal mass which is difficult to filter.
It is thus known to concentrate sugar beet hydrolysates by ultrafiltration, but these methods do not provide purified pectins.
DE Patent Specification 4 313 549 (Herbstreich and Fox KG Pektin FA) describes a method of preparing a pectin-containing extract from sugar beet material. In the method, the raw material is hydrolyzed with a citric acid solution at a temperature varying between 50xc2x0 C. and the boiling temperature of the solution.
U.S. Pat. No. 4,816,078 (Sxc3xcddeutsche Zucker-Aktiengesellschaft) describes the recovery of L-arabinose from sugar beet pulp or other vegetable material by basic hydrolysis, the L-arabinose being subsequently chromatographically purified. U.S. Pat. No. 5,250,306 (British Sugar PLC) discloses the recovery of araban from sugar beet pulp by first using basic hydrolysis and then ultrafiltration. In the basic hydrolysis according to this publication, pectin is destroyed and only sugars can be recovered.
WO 99/10542 (Cultor Corporation) describes the recovery of L-arabinose from sugar beet pulp using chromatographic separation with a cation exchanger in a monovalent form. This process includes, as a preceding step, extraction of sugar beet pulp with a strong alkaline solution. The use of strong alkali destroys pectin compounds, whereby only sugars are recovered.
The utilization of enzymes to degrade high molecular citrus pectins is known in the art. European Publication 868854 (Japan Tobacco Inc.) discloses a method of hydrolyzing citrus pectins so that the molecular weight is reduced to a range of about 20000 to 80000 Da. U.S. Pat. No. 5,472,952 (Squibb Bristol Myers Co.) describes a method to degrade citrus pectins to a molecular weight in a range of 3300 to 500000 in order to obtain a soluble fibre product. U.S. Pat. No. 5,952,308 (Pola Chem. Ind. Inc.) discloses a method of treating apple and citrus pectin with pectinase enzymes. The enzyme treatments are applied to separated high molecular weight pectins. The enzyme treatments are not carried out as a part of the separation/purification process in order to improve the process and the end product starting from sugar beet pulp.
The present invention provides a multistep purification/separation process for producing a high class sugar beet pectin suitable for drying and/or chemical or enzymatic modification simultaneously with high class sugar components such as L-arabinose. The whole purification/separation process takes place in an aqueous solution and the end products are pure aqueous solutions of pectin and pectic sugars/oligomers.
In connection with the present invention, pectins refer to polysaccharide compounds of high molecular weight being composed of partly methylated polygalacturonic acid chains (polygalacturonic acid content at least 65%). Pectin also contains araban, galactan and xylose side chains attached to the polygalacturonic acid chain, and rhamnoses interrupting the continuous polygalacturonic acid chain. Furthermore, the galacturonic acid groups of sugar beet pectin are partly acetylated.
In connection with the present invention, pectic sugars/oligomers refer to polysaccharides, oligosaccharides and mono- and disaccharides, such as arabans of low molecular weight, arabino-oligomers, arabinose, galactans, galactose, galacto-oligomers, rhamnose and fucose, which are present together with pectin in the sugar beet pulp after the sugar extraction. The sugar beet pulp to be treated may also contain small amounts of sucrose, glucose and fructose.
In connection with the present invention, sugar beet pulp refers to pulp which is obtained in connection with the production of sugar and which remains after sugar extraction and from which the sugars have to a large extent been extracted.
In connection with the present invention, the sugar beet pulp hydrolysate refers to hydrolyzed sugar beet pulp which contains pectins and pectic sugars/oligomers as well as salts to be separated and which is in the form of a solution.
In connection with the present invention, salts refer to small-molecular ionized substances, typically to inorganic small-molecular ionized substances such as sodium salts, potassium salts and calcium salts. Typically, the salts are the sodium, potassium and/or calcium salts of inorganic acids, such as hydrochloric acid, sulphuric acid and/or nitric acid. These are typically in salt form in a neutralized solution and in ion form in an acidic solution. The salts mainly originate from the pretreatment, such as acidic or basic hydrolysis and potential neutralization of sugar beet pulp.
The method of the invention has been successfully used for separating/purifying pectins and pectic sugars/oligomers into separate products while salts have simultaneously been removed from the pectins and pectic sugars/oligomers. The method in its entirety is conducted in an aqueous solution. This enables inflammability and toxicity problems relating to the use of organic solvents, such as isopropanol and ethanol, to be avoided.
Since the whole process is carried out in water solution, the pectin compounds are present in a soluble form throughout the procedure. This means a great advantage compared to earlier methods where the pectin is first separated by alcohol or metal precipitation and later redissolved in order to carry out necessary modifications.
The separation method used in the present invention is based on molecular weight fractionation, i.e. the fractionation is effected on the basis of different molecular weights of the components to be separated.
The pectin and pectic sugar/oligomer products recovered from the method of the invention can be used in foods and feeds as such. The products can also be dried e.g. by spray drying or modified by enzymatic or chemical methods to obtain other products. It is possible to modify the end product by adjusting the separation/purification process in order to produce taylor-made pectins with desired molecular weight. The produced pectins are of high purity providing clear, colour-free water solutions. The produced pectin products can be used as food ingredients, thickeners, emulsifiers, soluble fiber products and texturizers. The recovered pectic sugar products, such as L-arabinose products are useful as special sweeteners, for example.
Objects of the invention are achieved by a method which is characterized by what is set forth in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.